Method for protecting electronic components

ABSTRACT

An an electronic circuit having improved protection against harsh environments, a preferred embodiment thereof including: a substrate 10 having a top surface 12; an electronic component 14 attached to the top surface of the substrate; a plastic and metal foil laminated barrier 16 having an outer periphery 18 thereabout, the outer periphery being sealably attached to the top surface 12 of the substrate so as to define a closed pocket 20 between the top surface 12 and the barrier 16 within which the electronic component 14 is enclosed; and a desiccant element 50. The desiccant element 50 includes: a case 51 having an internal chamber, an inlet orifice 58, and an outlet orifice 59, wherein the inlet and outlet orifices are each in communication with the internal chamber; a predetermined amount of desiccant material 53 contained within the internal chamber; a normally-open interior valve 54 situated between the inlet orifice 58 and the internal chamber; a normally-closed exterior valve 56 situated between the outlet orifice 59 and the internal chamber; and heating means 52 for selectably heating the desiccant material 53 preferably above a regeneration temperature thereof. The desiccant element 50 is situated such that at least the interior orifice 54 thereof is sealably enclosed within the closed pocket 20.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to electronic circuits, and moreparticularly to a method for protecting electronic circuits againstharsh environments.

2. Disclosure Information

Many environments in which electronic circuits are used present harshconditions which are detrimental to the performance and/or lifeexpectancy of the circuit components. For example, in some automotiveapplications circuit components must be able to withstand severevibrations, drastic temperature fluctuations (e.g., between -40° C. and125° C.), corrosive and/or particle-laden exhaust fumes, highatmospheric moisture content, and so forth.

Various approaches are known for protecting electronic circuits fromsuch harsh environmental conditions. One such approach is to provide acover or housing of some sort around at least some portion of thecircuit. Another approach is to pot the whole circuit or portionsthereof in an epoxy, silicone, or other compound.

However, these and other previously known approaches often suffer fromone or more drawbacks. For example, potting a circuit may protect itfrom gross exposure to water and other harmful fluids, but typicallydoes not protect against gradual seepage of such fluids through thepotting material and into the electronics over time. Likewise, providinga cover or housing over or about the electronics may suffer the samedisadvantage. Furthermore, even if a cover or housing is generally wellsealed against water penetration, over time moisture may nonethelesspermeate into and accumulate in the interior of such covers or housings,which may detrimentally affect the functioning and/or useful life of thecircuit.

It would be desirable, therefore, to provide some means for protectingan electronic circuit against the above-mentioned harmful environmentalconditions without the aforementioned drawbacks.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of prior artapproaches by providing an electronic circuit having improved protectionagainst harsh environments. A preferred embodiment of the presentinvention comprises: a substrate having a top surface; an electroniccomponent attached to the top surface of the substrate; a plastic andmetal foil laminated barrier having an outer periphery thereabout, theouter periphery being sealably attached to the top surface of thesubstrate so as to define a closed pocket between the top surface andthe barrier within which the electronic component is enclosed; and adesiccant element. The desiccant element comprises: a case having aninternal chamber, an inlet orifice, and an outlet orifice, wherein theinlet and outlet orifices are each in communication with the internalchamber; a predetermined amount of desiccant material contained withinthe internal chamber; a normally-open interior valve situated betweenthe inlet orifice and the internal chamber; a normally-closed exteriorvalve situated between the outlet orifice and the internal chamber; andheating means for selectably heating the desiccant material above itsregeneration temperature. The desiccant element is situated such that atleast the interior orifice thereof is sealably enclosed within theclosed pocket.

It is an object and advantage that the present invention offers improvedprotection to electronic circuits against harsh environmentalconditions.

Another advantage is that a preferred embodiment of the presentinvention offers regeneratable hygrometric protection to electroniccircuits.

These and other advantages, features and objects of the invention willbecome apparent from the drawings, detailed description and claims whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-2 are elevation section views of a first embodiment according tothe present invention.

FIG. 3 is a perspective view of a desiccant element according to a firstembodiment of the present invention.

FIG. 4 is an elevation section view of a second, preferred embodimentaccording to the present invention.

FIG. 5 is a perspective view of a desiccant element according to asecond embodiment of the present invention.

FIGS. 6-7 are elevation section views showing methods for sealablyattaching a barrier periphery to a substrate top surface according tothe present invention.

FIG. 8 is a schematic diagram of a means for selectably switchingbetween two conditions according to a second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, FIG. 1 shows an electronic circuit havingimproved protection against harsh environments according to a firstembodiment of the present invention. The circuit comprises: a substrate10 having a top surface 12; an electronic component 14 attached to thetop surface 12 of the substrate 10; a plastic and metal foil laminatedbarrier 16 having an outer periphery 18 thereabout, with the outerperiphery 18 being sealably attached to the top surface 12 of thesubstrate 10 so as to define a closed pocket 20 between the top surface12 and the barrier 16 within which the electronic component 14 isenclosed; and a desiccant element 50 disposed within the pocket 20.

The desiccant element 50 comprises a predetermined amount of desiccantmaterial 53 contained within a case 51, as illustrated by FIG. 3. Thecase 51 may comprise a rigid housing made of plastic, metal, ceramic, orsome other material with apertures, screens, or other means therein forallowing the desiccant material 53 to absorb through the case 51 anymoisture present within the pocket 20, while preventing the desiccantmaterial 53 from spilling out of the case 51. The element 50 mightalternatively comprise a fine-mesh cloth bag or a water-permeablemembranous pouch with granular desiccant material contained therein;various other embodiments are also possible. The desiccant material 53may be any type of suitable desiccant which can be packaged within thecase 51, preferably in granular form. Examples of suitable materials 53include (but are not limited to) silica gel, SiO₂, CuSO₄, CaSO₄, CaCl₂,ZnBr₂, ZnCl₂, NaOH, CaBr₂, KOH, Al₂ O₃, CaO, BaO, Mg(ClO)₄, and P₂ O₅.

The desiccant element 50 may be attached to the top surface 12 of thesubstrate 10, to the interior surface of the barrier 16, or to bothAlternatively, rather than being attached to any adjacent structure, itmay instead be sandwiched between the top surface 12 of the substrate 10and the interior surface of the barrier 16 so as to be held in placetherebetween.

To provide additional structural support and protection, the circuit mayfurther comprise one or more support members 22, as shown in FIG. 2.Each support member 22 is situated within the closed pocket 20 so as tohave a first end contiguous with the top surface 12 of the substrate 10or a top surface of an electronic component 14 (or both), and a secondend contiguous with the interior surface 17 of the barrier 16. Suchsupports 22 are preferably made of foam, plastic, or some other materialwhich imparts additional crush-resistance and/or protection fromvibration to the electronic circuit.

The barrier 16 is a lamination of at least one layer of rigid orsemi-rigid plastic 16p and at least one layer of metal foil 16m. Theplastic 16p and metal foil 16m may be sheets that are adhered orotherwise bonded together, or they may be formed by overmolding theplastic onto one or both surfaces of the metal foil(s) (e.g., by placinga metal foil into a mold and then injecting molten plastic thereon ortherearound). Other well known methods are also available for providingthe plastic and metal foil laminated barrier 16. Although in a preferredembodiment the interior surface 17 of the barrier 16 is defined by ametal foil 16m and the exterior surface 19 is defined by a plastic layer16p, as shown in FIGS. 1-2, 4, and 6-7, it is likewise possible that theinterior surface 17 be defined by a layer of plastic 16p and/or that theexterior surface 19 be defined by a metal foil 16m.

As illustrated in FIG. 2, the barrier may further comprise a door means26 sealably disposed therein for permitting access into the pocket 20for removal and replacement of the desiccant element 50. The door means26 preferably includes an access door and means for sealably attachingthe door to the barrier in a substantially watertight closed position.The door means 26 may include an attachable hinge or molded-in hingejoint for pivotably connecting the door to the barrier.

The outer periphery 18 of the barrier 16 may be sealably attached to thetop surface 12 of the substrate 10 in a variety of ways, so as tosealably enclose the electronic component 14 and desiccant element 50within the closed pocket 20. One way is to ultrasonically bond the outerperiphery 18 to the substrate 10 (as illustrated in FIG. 1), whileanother approach is to adhesively bond the periphery to the substrateusing a sealable adhesive (as illustrated in FIGS. 2, 4, and 6). Anothermethod is to use a gasket means 40 sandwiched between the top surface 12and the periphery 18 in conjunction with a fastening means 42 forsealably attaching the barrier periphery to the substrate. The gasketmeans 40 may comprise a gasket made of silicone, neoprene, or otherwater-sealable material, whether applied in solid form (e.g.,pre-molded) or in a liquid/gelatinous/extrudable form (e.g.,room-temperature-vulcanizing silicone caulk). The gasket means 40 shouldtypically define a closed loop generally conforming to the shape of theouter periphery 18. The fastening means 42 may include washer and screwarrangements (as illustrated in FIG. 7), nut-and-bolt combinations,clips, snap-fit joints, hook-and-loop fasteners, adhesives, and thelike. This gasket means/fastening means approach has the advantage thatthe barrier 16 may be removed and replaced as desired, such as whenrepairs or tests need to be conducted upon the electronics, or whenreplacing the desiccant element 50 if no door means 26 is provided.Whatever method is used, it is preferred that the attachment methodprovide a substantially water-tight seal about the periphery of theclosed pocket 20.

With the laminated barrier 16 sealably attached to the substrate 10 andenclosing the electronic component(s) 14 and desiccant element 50therein, improved mechanical, vibrational, and hygrometric protection isprovided to the component(s) 14 and the associated circuit elements andinterconnects (e.g., solder joints, circuit traces, jumper wires, etc.).Protection may be further enhanced by constructing the barrier 16 usingone or more rigid or semi-rigid plastic layers 16p therein. The rigidityof the layer(s) 16p will depend upon the resin material used, thethickness of each layer, the use of ribs or other molded-in or attachedstructural members, the geometry of the barrier, etc. For example, atypical barrier 16 may comprise a 0.125- to 0.250-inch-thick sheet ofacrylonitrile-butadiene-styrene (ABS), polyetherimide, polyethersulfone,or some other polymer, to which a 0.01- to 0.05-inch-thick sheet ofaluminum foil has been attached. Additional protection is offered byproviding the support members 22 described above, which may beconstructed out of styrene foam, for example.

With the periphery 18 of the barrier being sealably attached to thesubstrate 10, the closed pocket 20 may be made generally water-tight.The electronics may be further protected from humidity by the metal foil16m; whereas some microleakage of moisture may occur through the plasticlayer 16p, substantially no water may pass through the metal foil 16m.(The metal foil 16m may also provide some degree of EMI protection forthe electronics.) Additionally, the desiccant element 50 serves toabsorb any moisture which might find its way into the pocket 20, such asby seepage past any breaks in the seal about the door means 26 orthrough microfissures in ultrasonically welded outerperiphery-to-substrate joints and seams. The element 50 can beperiodically removed and replaced with a new element 50 through the doormeans 26.

A second, preferred embodiment of the present invention is illustratedin FIG. 4. Like the first embodiment, the present embodiment includes asubstrate 10 having a top surface 12; an electronic component 14attached to the top surface 12 of the substrate 10; a plastic and metalfoil laminated barrier 16 having an outer periphery 18 sealably attachedto the top surface 12 of the substrate 10 so as to define a closedpocket 20 therebetween within which the electronic component isenclosed; and a desiccant element 50. However, whereas the entiredesiccant element 50 in the first embodiment was sealably enclosedwithin the closed pocket 20, only a portion of the element 50 in thepresent embodiment is so enclosed. Furthermore, the present element 50includes additional structure not necessarily found in that of theprevious embodiment.

As can be seen from FIG. 4, the desiccant element 50 of the presentembodiment comprises: a case 51 having an internal chamber, an inletorifice 58, and an outlet orifice 59, wherein the inlet and outletorifices are each in communication with the internal chamber; apredetermined amount of desiccant material 53 contained within theinternal chamber; a normally-open interior valve 54 situated between theinlet orifice 58 and the internal chamber; a normally-closed exteriorvalve 56 situated between the outlet orifice 59 and the internalchamber; and heating means 52 for selectably heating the desiccantmaterial 53 to a temperature preferably above a regeneration temperaturethereof. The desiccant element 50 is situated such that at least theinterior orifice 54 thereof is sealably enclosed within the closedpocket 20.

As illustrated in FIGS. 4 and 5, the heating means 52 may comprise aheat conducting conduit portion 52c disposed within and/or about thecase 51 in direct or indirect thermal contact with the desiccantmaterial 53, wherein the heat conducting conduit portion 52c has inletand outlet ports 52i/52o capable of sealable fluid communication withrespective inlet and outlet conduits 31/32 as shown. The inlet andoutlet conduits 31/32 may be sealably connected at one end to theirrespective inlet and outlet ports 52i/52o (via clamps, o-rings,fittings, etc.) and at the other end to a circulating pump. A heatedfluid (e.g., radiator fluid, water, oil, exhaust gas, etc.) may becirculated through the inlet 31/52i, into the conducting portion 52c,and out through the outlet 32/52o so as to elevate the desiccant 53 to atemperature preferably at or above its regeneration temperature.Alternatively, the heating means 52 may comprise an electric resistanceheating element within and/or about the case 51 which may beelectrically activated by a power source external to the circuit.

The circuit may further include means 60 for selectably switching theinterior valve 54, the exterior valve 56, and the heating means 52between (1) a normal operating condition and (2) a regeneratingcondition. In the normal operating condition, the interior valve 54 isopen, the exterior valve 56 is closed, and the heating means 52 isde-activated (i.e., not supplying heat). In this condition, thedesiccant material 53 is in water-absorbable communication with theinterior of the pocket 20, so that the material 53 may absorb moisturetherefrom and keep the pocket 20 desirably dry. When the moisturecontent of the desiccant material 53 is above a predetermined level, orwhenever otherwise desired, the circuit may be switched to theregenerating condition. In this condition, the interior valve 54 isclosed, the exterior valve 56 is open, and the heating means 52 isactivated, thus closing off communication between the desiccant material53 and the interior of the pocket 20 and opening up water-releasablecommunication between the material 53 and the outside environment. Withthe heating means 52 activated, the desiccant material 53 may be heatedup preferably above its regeneration temperature so as to liberate thepreviously absorbed moisture from the material 53 out to the atmosphere.Once the moisture content of the material 53 is below a predeterminedlevel, or whenever otherwise desired, the circuit may be switched backto the normal operating condition, wherein the desiccant element 50 mayonce again work to absorb moisture from the interior of the closedpocket 20. With these two conditions switchably provided, the presentembodiment offers the advantage of having a regeneratable desiccantelement.

The means 60 for selectably switching may comprise mechanical,electrical, pneumatic (i.e., pressure or vacuum), fluidic, hydraulic,microprocessor, and/or other means 62/64/66 for physically opening andclosing the inlet and outlet valves 54/56 and for activating andde-activating the heating means 52. For example, as illustrated in FIGS.4, 5, and 8, the means 60 may comprise vacuum lines 55/57 connectedupstream to vacuum means 62/64 (e.g., portions of an automotive enginevacuum system) for opening and closing the interior and exterior valves54/56 as needed, and inlet and outlet fluid lines 31/32 connectedupstream to a fluid circulating means 66 (e.g., an automotive engineradiator fluid pump) for activating and de-activating a heating conduit52c within the case 51. A central control means 61 (e.g., amicroprocessor or control circuit) may be used to coordinate theactuation of the means 62/64/66 in order to selectably switch betweenthe normal operating and regenerating conditions. The control means 61may include microprocessor or other means for automatically switchingthe circuit back-and-forth between the two conditions based on whetherthe desiccant moisture content level is above or below a predeterminedthreshold value (e.g., 85% of maximum absorptive capacity). The centralcontrol means 61 may also include an operator switch 68 which may beused by a human operator to selectably switch back-and-forth between thetwo conditions as desired, and/or a condition indicator 69 whichindicates which of the two conditions the circuit is presently in.

The circuit may further comprise a moisture content sensor 70 within thecase 51 in communication with the desiccant material 53 so that thehygrometric condition of the material 53 may be sensed. This sensor 70may in turn be connected to an indicator 72 for indicating thehygrometric condition of the desiccant, and/or it may be connected tothe means 60 for selectably switching.

Many different types of desiccant material 53 may be used in eitherembodiment of the present invention, and may be selected based on suchfactors as cost, regeneration temperature, regeneration efficiency,expected service life, and the like. For example, a common silica gelmaterial having a typical regeneration temperature of 160° C. may bemore cost effective for most applications than a CaSO₄ material having a250° C. regeneration temperature.

Various other modifications to the present invention will, no doubt,occur to those skilled in the art to which the present inventionpertains. For example, although the barrier 16 is described herein asbeing attached to a "top" surface 12 of the substrate 10, thedesignation of "top" has been made arbitrarily, since either side of asubstrate 10 may be deemed as the "top" surface. Thus, the presentinvention also covers application to what might appear to be, or whatmight otherwise be designated as, a "bottom" surface of a substrate 10.Also, it should be apparent that the "thermal contact" referred to abovebetween the heat conducting conduit portion 52c and the desiccant 53does not require direct contact therebetween; the conduit 52c anddesiccant 53 may be indirectly in contact with one another with one ormore intervening, thermally conductive elements (e.g., heat pipes)interposed therebetween. Moreover, it should be apparent that thesubstrate 10 as used herein is not limited to conventional, flat, planarFR-4 epoxy/glass substrates, but may also include housings, covers,shrouds, panels, doors, and any other member providing asurface--whether planar or non-planar--on which electronic componentsmay be mounted; such substrate may be rigid or flexible, and may beconstructed of polymer, metal, ceramic, or any combination thereof.Also, it should be understood that the term "desiccant" may refer to anymaterial having hygroscopic characteristics. Additionally, although itis preferable that the desiccant material of the preferred embodiment beheated to a temperature at or above its regeneration temperature, thoseskilled in the art will recognize that any increase in temperature--evento a temperature below the material's regeneration temperature--willprovide some regenerative effect (i.e., moisture will be liberatedtherefrom). It is the following claims, including all equivalents, whichdefine the scope of the present invention.

What is claimed is:
 1. An electronic circuit having improved protectionagainst harsh environments, comprising:a substrate having a top surface;an electronic component attached to said top surface of said substrate;a plastic and metal foil laminated barrier having an outer peripherythereabout, said outer periphery being sealably attached to said topsurface of said substrate so as to define a closed pocket between saidtop surface and said barrier within which said electronic component isenclosed; and a desiccant element comprising:a case having an internalchamber, an inlet orifice, and an outlet orifice, wherein said inlet andoutlet orifices are each in communication with the internal chamber; apredetermined amount of desiccant material contained within the internalchamber; a normally-open interior valve situated between the inletorifice and the internal chamber; a normally-closed exterior valvesituated between the outlet orifice and the internal chamber; andheating means for selectably heating said desiccant material; whereinsaid desiccant element is situated such that at least the interiororifice thereof is sealably enclosed within the closed pocket.
 2. Anelectronic circuit according to claim 1, wherein said barrier comprisesat least one layer of plastic and at least one layer of metal foil. 3.An electronic circuit according to claim 1, wherein said desiccantelement is attached to at least one of the substrate and the barrier. 4.An electronic circuit according to claim 1, wherein said desiccantelement is sandwiched between the top surface of said substrate and saidbarrier.
 5. An electronic circuit according to claim 1, furthercomprising at least one support member contiguous at a first end withthe top surface of said substrate and contiguous at a second end withsaid barrier.
 6. An electronic circuit according to claim 1, furthercomprising at least one support member contiguous at a first end with atop surface of said electronic component and contiguous at a second endwith said barrier.
 7. An electronic circuit according to claim 1,wherein said outer periphery is ultrasonically bonded to the top surfaceof said substrate so as to sealably enclose said electronic componentand said desiccant element within the closed pocket.
 8. An electroniccircuit according to claim 1, wherein said outer periphery is adhesivelybonded to the top surface of said substrate so as to sealably enclosesaid electronic component and said desiccant element within the closedpocket.
 9. An electronic circuit according to claim 1, furthercomprising:gasket means sandwiched between the top surface of saidsubstrate and the outer periphery of said barrier; and fastening meanscooperating with said gasket means for attaching the outer periphery ofsaid barrier to the top surface of said substrate.
 10. An electroniccircuit according to claim 1, further comprising a door means sealablydisposed in said barrier for permitting access into the pocket forremoval and replacement of said desiccant element.
 11. An electroniccircuit according to claim 1, wherein said desiccant element comprises apredetermined amount of desiccant material contained within a case,wherein said desiccant material may absorb through said case anymoisture present within the pocket.
 12. An electronic circuit accordingto claim 1, wherein said desiccant material is selected from the groupconsisting of silica gel, SiO₂, CuSO₄, CaSO₄, CaCl₂, ZnBr₂, ZnCl₂, NaOH,CaBr₂, KOH, Al₂ O₃, CaO, BaO, Mg(ClO)₄, and P₂ O₅.
 13. An electroniccircuit according to claim 1, further including means for selectablyswitching said interior valve, said exterior valve, and said heatingmeans between:a normal operating condition, wherein said interior valveis open, said exterior valve is closed, and said heating means isde-activated; and a regenerating condition, wherein said interior valveis closed, said exterior valve is open, and said heating means isactivated.
 14. An electronic circuit according to claim 13, wherein saidmeans for selectably switching includes at least one of:a microprocessormeans for automatically switching back-and-forth between the normaloperating condition and the regenerating condition based on whether adesiccant moisture content level is above or below a predeterminedthreshold value; an operator switch which may be used by a humanoperator to selectably switch back-and-forth between the normaloperating and regenerating conditions as desired; and a conditionindicator which indicates which of the normal operating and regeneratingconditions the circuit is in.
 15. An electronic circuit according toclaim 1, wherein said heating means comprises:an inlet port and anoutlet port, each attached to said case and capable of sealable fluidcommunication with respective inlet and outlet conduits; and a heatconducting conduit portion disposed within said case in thermal contactwith said desiccant material, said portion being in sealable fluidcommunication with each of said inlet and outlet ports.
 16. Anelectronic circuit according to claim 1, wherein said heating meanscomprises an electric heating element disposed within or about said casein thermal contact with said desiccant material.
 17. An electroniccircuit according to claim 1, further comprising a moisture contentsensor disposed within said case in communication with said desiccantmaterial.
 18. An electronic circuit according to claim 17, wherein saidmoisture content sensor is connected to at least one of an indicator forindicating the hygrometric condition of said desiccant material, andsaid means for selectably switching between said normal operatingcondition and said regenerating condition.
 19. An electronic circuithaving improved protection against harsh environments, comprising:asubstrate having a top surface; an electronic component attached to saidtop surface of said substrate; a plastic and metal foil laminatedbarrier having an outer periphery thereabout, said outer periphery beingsealably attached to said top surface of said substrate so as to definea closed pocket between said top surface and said barrier within whichsaid electronic component is enclosed; and a desiccant elementcomprising:a case having an internal chamber, an inlet orifice, and anoutlet orifice, wherein said inlet and outlet orifices are each incommunication with the internal chamber; a predetermined amount ofdesiccant material contained within the internal chamber; anormally-open interior valve situated between the inlet orifice and theinternal chamber; a normally-closed exterior valve situated between theoutlet orifice and the internal chamber; heating means for selectablyheating said desiccant material above a regeneration temperaturethereof; wherein said desiccant element is situated such that at leastthe interior orifice thereof is sealably enclosed within the closedpocket; and wherein said interior valve, said exterior valve, and saidheating means may be switched between: a normal operating condition,wherein said interior valve is open, said exterior valve is closed, andsaid heating means is de-activated; and a regenerating condition,wherein said interior valve is closed, said exterior valve is open, andsaid heating means is activated.